In a medium saucepan, whisk together the granulated sugar, corn starch, and a pinch of salt.
In another bowl, combine the eggs and egg yolks until well mixed.
Gradually add the milk to the sugar mixture, stirring constantly over medium heat until it thickens and begins to bubble. Remove from heat.
Stir in the sweetened condensed milk, vanilla extract, and softened butter into the custard. Mix until smooth and well combined.
Allow the mixture to cool slightly at room temperature.
In your chosen pan, start by placing a layer of Palmier cookies at the bottom.
Pour a portion of the custard over the cookies, spreading it evenly.
Repeat the layering process: another layer of cookies, followed by custard, until all ingredients are used, finishing with a custard layer on top.
Cover the cake with plastic wrap and place it in the refrigerator for at least 4 hours, or overnight for best results.
Once chilled, carefully release the sides of the springform pan.
Top the cake with fresh berries for a beautiful presentation.
Slice and serve chilled, reveling in the creamy, cookie layers of this exquisite dessert.